Process for relaxing filamentary material



y 1969 r L D. CHIRGWIN. JR 3,443,009

PROCESS FOR RELAXING FILAMENTARYMATERIAL Filed Aug. 17, 1964 Sheet of 2 INVENTOR. LESTER D. CHIRGWIN,JR.

A TTORNEY Sheet 3 of 2 May 6, 1969 D. CHIRGWIN, JR

PROCESS FOR RELAXING FILAMENTARY MATERIAL Filed Aug. 17, 1964 INVENTOR. LESTER D. CHIRGWIN, JR.

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ATTORNEY United States Patent 3,443,009 PROCESS FOR RELAXING FILAMENTARY MATERIAL Lester Daniel Chirgwin, Jr., Stamford, Conn., assignor to American Cyanamid Company, Stamford, Conn., a corporation of Maine Filed Aug. 17, 1964, Ser. No. 389,833 Int. Cl. D021 13/00 US. Cl. 264-342 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved process for relaxing or retracting synthetic filamentary material by a continuous process and to apparatus for performing such process. More particularly, this invention relates to such process and apparatus wherein endless lengths of filamentary material, such as a tow, are treated with a turbulent flow of heated gas moving generally parallel to the direction of motion of such filamentary material through a confined zone.

The term tow as used herein is intended to refer to a rather large bundle of endless filaments disposed substantially parallel to each other without any interconnecting means preventing easy separation of any given filament or group thereof from the remainder of the bundle. Such a tow may comprise a bundle of as few as several thousand filaments up to several million or more as is well known in the production of synthetic yarns.

In the preparation of fibers of synthetic materials, it is common practice to provide a step wherein such fibers are elongated under tension in order to orient the polymer molecules within such fibers. Illustrative of such fibers are those made from such polymers as the polyamides, polyesters, cellulose triacetate, arcylonitrile polymers, et-c. Frequently, it is necessary or desirable to provide a heat treatment step for the purpose of relaxing or retracting such fibers in order to ease the strains introduced in the preceding orientation step and to develop better textile properties in such fibers. Also, such heat treatment serves to reduce the potential shrinkability of such fibers. Prior to the present invention, the desirability of such heat treatment was well known in the synthetic fiber industry and several techniques had been developed to accomplish this result.

One of these techniques for retracting or relaxing endless lengths of synthetic fibers involved the use of radiant heat. Illustrative of such technique is US. Patent 2,558,733 issued July 3, 1951, to Cresswell and Wizon wherein a small bundle of filaments is continuously passed lengthwise through a solt in a heat-treating furnace. This reliance on radiant heat for retracting fibers suffers several drawbacks. In the process of retracting fibers, substantial shrinkage of the fibers is usually desired which means that the endless length thereof must be under very low tension. When filamentary material is conducted through space under very low tension, there is a tendency for the material to flutter, causing it to approach toward and recede from the heated surface of the radiant heater. Since the amount of heat received by the fiber is a function of its distance from its source of radiant energy, it is readily apparent that this fluttering motion will cause very uneven heating of the filamentary material and, therefore, cause non-uniform retraction. Also, this technique is useless for processing a tow since the surface filaments will shield the filaments within the tow bundle from the source of radiant energy preventing them from being heated as much as the surface fibers.

It is also known to heat endless lengths of continuous filaments by passing them in contact with heated metal surfaces, such as around rotating heated rolls or across the surfaces of curved heated metal platens. Retraction is extremely difficult under either of these circumstances when dealing with a bundle of a very few fibers since the fibers are restricted in retraction while in contact with the heated metal rolls on which they are wound and the frictional drag when such filaments are pulled across curved heated metal platens serves to limit retraction or even produces elongation. Further, the low tensions involved in retraction operations results in uneven contact with and heat transfer from the heated metal surfaces, making uniformity of retraction difficult to achieve. Also, this technique is extremely difficult or impossible when dealing with a tow of synthetic fibers since the heat is transferred by conduction from the heated metal surface of the heater to the filaments which are in contact therewith at a relatively high rate of speed, while the heat is transferred very slowly, if at all, to those filaments which are in the tow bundle remote from contact with the heated metal surface.

In order to process a tow of synthetic fibers, one technique in use for retracting these fibers is to expose them to the action of saturated or wet steam under superatmospheric pressure. This can be done in a batch process in an autoclave, with all of the disadvantages attendant upon disrupting an otherwise continuous process to perform a batch-wise operation in the middle thereof. Alternatively, such steaming operation can be performed continuously in a pressurized chamber while the endless lengths of continuous filaments are temporarily stored on a moving conveyor belt, as illustrated in U.S. Patent 3,118,154 issued Jan. 21, 1964, to Osban and Carmen and US. Patent 3,037,369 issued June 5, 1962, to Leins and Osban. This technique, which produces satisfactory retraction of such fibers on a continuous basis, suffers certain practical disadvantages. Since such steamers are operated under a pressure considerably above atmospheric, pressure seals are required on the inlet and outlet thereof in order to permit continuous entrance and exit of the endless length of the material being treated while minimizing or eliminating the leakage of steam therethrough. Pressure seals for such a purpose have been developed having various degrees of effectiveness for such purpose and varying degrees of complexity of construction, as taught in US. Patent 3,046,773 issued July 31, 1962, to Healey; US. Patent 3,126,724 issued Mar. 31, 1964, to Kolonits; and US. Patent 3,137,151 issued June 16, 1964, to Yoshiike. The use of such apparatus also introduces considerable difficulty in clearing out any tangles which may develop within the hot sealed vessel during upsets in operations, since the interior thereof is not readily accessible to persons operating such equipment, Also, in the operation of such equipment, there is no positive control over the amount of the retraction permitted since the fibers are always completely free to retract as much as possible under the steaming conditions subject only to very slight frictional restraint of the fibers moving past each other on the conveyor belt during retraction.

It is also known to relax or retract endless lengths of continuous filaments on a continuous basis by the use of superheated water under superatmospheric pressure as described in U.S. Patent 3,027,740 issued Apr. 3, 1962, to Sonnino. Since this operation also requires a closed pressurized chamber, the same problems exist as were described above in connection with the use of wet or saturated steam under superatmospheric pressure. In addition, the heavy weight of adherent liquid tends to reduce substantially the amount of retraction produced in such operation due to restretching the tow when it is lifted from the superheated water wherein the retraction occurs.

Attempts have been made to eliminate the problems connected with the foregoing relaxation or retraction techniques by the use of chemical agents to perform this operation. For example, heated aqueous acetic acid solution can be used for relaxing dried acrylic fibers as taught in U.S. Patent 3,083,071 issued Mar. 26, 1963, to M. Wishman. Also, as described therein, swelling agents or solvents for fibers have been known as relaxation or retraction agents for treating synthetic fibers. Generally speaking, such materials introduced the problem of concentration control in addition to temperature control in operations designed to produce uniformity of product. Also, such processes must always be followed by washing and drying of these fibers to remove these additional chemical-s from such fibers and therefore they involve the added expenses incurred in purchase and/or recovery of these chemical agents.

The present invention overcomes all of the foregoing difficulties in all of the previously known relaxation or retraction processes by providing a process which is very rapid, is useful for retracting or relaxing tow bundles of any number of filaments, which is simple in operation, and which does not require complex equipment while producing a highly uniform relaxation which is controllable at any level of retraction up to the maximum possible with the fibers being treated.

Briefly, the present invention provides a new method and apparatus for continuously relaxing filamentary material which comprises continuously passing an endless length of the filamentary material lengthwise through an elongated confined zone while concomitantly heating the filamentary material solely by exposure to hot gas flowing in turbulent fiow longitudinally through the elongated confined zone. Thus, the direction of movement ofthe filamentary material and the general direction of flow of the hot turbulent gas are generally parallel.

In order to perform this method, the endless length of filamentary material is continuously passed lengthwise through an elongated chamber or confined zone, which may be of the nature of a pipe open at both ends. Into one end of this chamber is introduced heated gas, such as heated air, at relatively high velocity (moving in turbulent flow) through a specially bafiied entranceway so that the general motion of this turbulent gas is substantially parallel to the axis of the chamber through which the filamentary material is passing.

This chamber preferably is mounted with its axis vertical, with the filamentary material and the hot turbulent gases both moving concurrently in an upward direction for maximum retraction. However, it is possible to perform the method of the present invention by the use of apparatus wherein the flow of heated gas is countercurrent to the direction of movement of the filamentary material or wherein both of these movements are downward. Also, it is possible to have the elongated chamber mounted so its axis is other than vertical (e.g., horizontal) for the performance of the present method.

In the performance of the present invention, the degree of retraction possible, for any given fiber composition and previous history, is a [function of the time and temperature of the retraction treatment. It is necessary that the tow bundle be exposed to the heated gases for a minimum time which is sufficient to transfer enough heat from the turbulent gas to the filamentary material to produce the desired retraction or relaxation while avoiding the use of a time which is sufficiently long to degrade the fibers at the elevated temperature to which it is being exposed. The temperature of the heated gas which flows in turbulent flow through the confined zone for heating up the filamentary material must be at a temperature which is sufficiently high to produce effective retraction or relaxation but it should not be so high as to melt the outside fibers of the tow bundle or degrade the fibers being treated. Thus, numerical limits on the time and temperature of this operation cannot reasonably be set forth since the time and the temperature depend upon each other and upon the fiber composition. However, within the framework set forth above, suitable time and temperature conditions may readily be determined for any given application since the combined effect of the time and temperature must be sufficient to cause the desired retraction or relaxation without seriously degrading the fibers. A time of between about 0.1 second and 30 seconds with a temperature between about 250 F. and about 600 F. for the hot turbulent gas as it enters the confining chamber have been found to be satisfactory for the treatment of acrylic fibers which had previously been dried and were moving concurrently with the fiow of the heated turbulent gas. Preferably, about 0.5 to about 5.0 seconds of contact with turbulent gas at a temperature of between about 400 F. and 550 F. can be used for optimum retraction of acrylic fibers.

The movement of the endless length of filamentary material through the confining zone wherein the retraction occurs can be effected by passing the filamentary material around or between rolls located near the inlet end of the confining zone which feed the filamentary material to rolls located near the outlet end of the confining zone. In order to permit retraction, the outlet rolls are rotated at a peripheral speed which is lower than the peripheral speed of the inlet rolls. Control of the relative speeds of these two sets of rolls controls the degree of retraction permitted, which may be any value less than the maximum retraction possible. Thus, if the conditions are such that the maximum retraction possible is 50% of the length of the fiber being treated, the relative speeds of these two sets of rolls may be so adjusted as to produce 40% retraction, 20% retraction, 8% retraction, relaxation at 0% retraction or relaxation at constant length, etc.

The gas moving through the confined zone for heating up the filamentary material being retracted may move at any velocity within a wide range of conditions. The velocity must be sufficient to produce adequate turbulence for effective transfer of heat to all of the fibers within the tow bundle but should not be enough to seriously disarrange the tow bundle or to restretch the filaments by frictional drag when maximum retraction is desired. This velocity range is therefore a function of apparatus design and the size of the tow bundle as well as being a function of the tension generated between the aforementioned two sets of rolls used to control the degree of retraction permitted. Thus, where maximum retraction is desired and minimum tension results between the inlet rolls and the outlet rolls, lower gas velocities would be used than where higher tensions are applied to limit the amount of retraction during relaxation. When maximum retraction is desired using a confined chamber wherein the continuous filaments and the hot turbulent gas move co-currently in an upward direction, it is preferred that the gas velocity be substantially equal to the sum of the velocity neces sary to float the tow and the lengthwise velocity of the endless filaments through the retraction unit. This gas velocity can be readily determined for any particular operation by varying the gas velocity until the tension on the filaments exiting from the confined chamber is reduced to about zero and the tension on the filaments entering the confined chamber is minimized.

For best operation, the fibers should be dry when introduced into the confining zone for retraction. Otherwise, the heat load for evaporation of variable amounts of moisture contained in the tow would be too variable to permit satisfactorily uni-form retraction by the use of this process since the heating medium (heated gas) has a relatively low heat capacity compared with the demands made when water must be evaporated from wet fibers. This highly variable heat load would result in extremely non-uniform retraction. In order to minimize the tendency of the dry fibers to fuse together during this process, the filaments in the tow should contain a suitable lubricant thereon. A listing of suitable lubricants for this high temperature operation with acrylic fibers may be found in column 5 lines 1 through 28 of US. Patent 3,130,249 issued Apr. 21, 1964, to Wishman and Preece.

It has been observed that occasionally acrylic fibers are darkened slightly under certain processing conditions within the framework of the present invention. When this is observed, it frequently can be minimized by the application of antioxidants to the fibers prior to retraction. Illustrative of the antioxidants which have been found useful are: 2,6-ditertiary-butyLp-cersol, butylated hydroxy tolulene (BHT), butylated hydroxy anisole (BHA), 2,2- thiobis-(4-methyl-6-tertiary-butylphenol), 2,2'-methylenebis-(4-methyl-6-tertiary-butylphenol), propyl gallate (with or without citric acid), p-methoxy phenol (hydroquinone monomethyl ether), catechol, isoascorbic acid, and hydroquinone monobenzyl ether.

In order to further prevent fiber degradation and restretching of the fibers on further processing, it sometimes is desirable to quench the fibers exiting from the confined zone of the retraction unit to minimize the time of exposure to elevated temperature. This quenching may be accomplished by cold or ambient air, water, or other fluid.

The present process is useful for retraction of a tow having any number of filaments up to one million or more. When large tows are being treated, it is preferred that the tow bundle have a cross-section which is relatively ribbon-like rather than one which is relatively ropelike (i.e., preferably a cross-section which is relatively flat rather than relatively round) in order to facilitate the transfer of heat uniformly to all filaments within the tow bundle from the hot turbulent gases.

For a clearer and more detailed understanding of the present invention, reference may be had to the accompanying drawings wherein:

FIG. 1 is a perspective view of an embodiment of apparatus according to the present invention;

FIG. 2 is a vertical cross-sectional view of the upper portion of the apparatus illustrated in FIG. 1;

FIG. 3 is a vertical cross-sectional view of the lower portion of the apparatus illustrated in FIG. 1;

FIG. 4 is a cross-sectional view taken on the line IVIV of FIG. 3; and

FIG. 5 is a plan view of a cover plate.

In the embodiment of apparatus for performing the method of the present invention illustrated in the accompanying drawings, the apparatus comprises generally an elongated tube-like confining chamber 11 through which the endless length of filamentary material in the form of an endless tow 13 is passed in an upward direction by means of inlet rolls 15 and outlet rolls 16. Concomitantly with the passage of endless tow 13 longitudinally through chamber 11, hot turbulent gas is also passed longitudinally through chamber 11 in an upward direction by means of blower 18 and heater 19 which are connected in a closed loop with chamber 11 by means of conduits 20, 21. If desired, conduit 20 may be provided with a valved opening into which ambient air may be drawn when found necessary or desirable for smoothness of operation of the entire retraction unit.

As illustrated in FIGS. 3 and 4, suitable bafiling arrangement is provided in the lower portion of chamber 11 to provide a turbulent flow of hot gas which will move longitudinally through chamber 11. It is important for the performance of this method and the operation of this apparatus that any tendency of the hot turbulent gas to swirl and move helically through chamber 11 be minimized. Accordingly, the bottom end of chamber 11 is provided with a closure plate 24 to which is secured a central tube 25 which is mounted coaxially with chamber 11 around opening 23 in plate 24. Central tube 25 extends upwardly to a point above the opening where conduit 21 enters chamber 11, and downwardly to opening 23 in closure plate 24 through which tow 13 enters chamber 11. Mounted in the upper portion of the annulus between central tube 25 and the wall of chamber 11 are a plurality of tubular bafile members 26 which extend parallel to the axis of chamber 11 from the upper end of central tube 25 toward the top of the opening where conduit 21 enters chamber 11. Thus, heated gas entering chamber 11 from conduit 21 is distributed around the periphery of chamber 11 and directed upwardly in a direction substantially parallel to the axis of chamber 11 with a minimum of swirling.

A short distance above the upper end of central tube 25, chamber 11 is provided with a bafile plate 28 which is provided with an orifice 29 which is centrally disposed in the path through which tow 13 and heated gas must pass in rising through chamber 11. The relatively small size of orifice 29 causes the heated gas to flow radially inwardly towards the axis of chamber 11 immediately below baffle plate 28 and then outwardly above baflle plate 28. This non-swirling radial motion of the heated turbulent gas serves to permit uniform contact between the heated gas and all the filaments in tow bundle 13 so as to permit uniform and rapid heat transfer and retraction of the tow 13.

As illustrated in FIG. 2 a somewhat simpler bafiling arrangement is provided in the upper portion of chamber 11. This bafile, which serves to separate the spent gas exiting through conduit 20 from tow 13 exiting from chamber 11 towards outlet rolls 16, mainly comprises a closure plate 31 provided with a central opening 32 from which depends a central tube 33, the lowermost end of which extends to below the opening where conduit 20 exits from chamber 11. If found necessary, the upper end of chamber 11 may also be provided with a plurality of tubular baffle members disposed in a manner similar to that of tubular batlle members 26 in the lower end of chamber 11. However, this extra bafiling is usually unnecessary for the prevention of swirling motion of the hot turbulent gas passing through chamber 11.

To reduce expiration and inspiration of gases through the openings 23 and 32 at the ends of chamber 11, removable plates 35 may be used. As best seen in FIG. 5, each cover plate 35 is provided with a large centrally disposed slot 36 through which tow bundle 13 can pass with adequate clearance when cover plates 35 are in place. Cover plates 35 are each provided with a pair of fastening slots 37 which are suitably positioned to coact with fastening bolts 38 which are threaded into closure plates 24 and 31. These cover plates 35 are normally removed from the ends of chamber 11 until after tow 13 has been threaded through from inlet rolls 15 to outlet rolls 16, after which cover plates 35 are slid across the ends of chamber 11 with the fastening slots 37 surrounding bolts 38 and the centrally disposed slot 36 surrounding tow 13. When suitably positioned, bolts 38 are tightened securing cover plates 35 in position.

Other obvious modifications exist for the structures specifically illustrated and described herein, and, to the extent they embody the principles of the present invention as defined in the subjoined claims, such modifications are intended to be included within the scope and range of equivalents of the subjoined claims.

I claim:

1. The method of continuously retracting filamentary material comprising continuously feeding endless lengths of said filamentary material substantially vertically upward into the lower portion of a confined zone at a first linear velocity and continuously removing said filamentary material from the upper portion of said confined zone at a second linear velocity lower than said first linear velocity while concomitantly heating said filamentary material solely by exposure to hot gas flowing substantially vertically upward in turbulent flow through said confined zone.

2. The method of continuously retracting filamentary material comprising continuously feeding endless lengths of said filamentary material substantially vertically upward into the lower portion of a confined zone at a first linear velocity and continuously removing said filamentary material form the upper portion of said confined zone at a second linear velocity lower than said first linear velocity while concomitantly heating said filamentary material solely by exposure to hot gas flowing substantially vertically upward in turbulent flow through said confined zone for a time and at a temperature sulficient for said filamentary material to retract but not sufiicient to materially degrade said filamentary material.

3. The method of continuously relaxing a tow of filamentary material comprising continuously feeding endless lengths of dry lubricated filamentary material in the form of a relatively ribbon-like tow band substantially vertically upward through an elongated confined zone while concomitantly heating said material solely by exposure to hot gas flowing in turbulent fiow substantially vertically upward through said elongated confined zone, and then cooling the thus heated and relaxed filamentary material.

4. The method of continuously relaxing a tow of filamentary material comprising continuously feeding endless lengths of dry lubricated filamentary material in the form of a relatively ribbon-like tow band substantially vertically upward through an elongated confined zone while concomitantly heating said material for a time and at a temperature sufiicient for said filamentary material to retract but not sufficient to materially degrade said filamentary material solely by exposure to hot gas flowing in turbulent flow substantially vertically upward through said elongated confined zone, at a velocity suflicient to produce adequate turbulence for uniform and elfective heat transfer but less than that at which said filamentary material is seriously disarranged or substantially elongated and then cooling the thus heated and relaxed filamentary material.

5. A method of continuously relaxing filamentary material, comprising continuously exposing, for a time and at a temperature suflicient for said fiilamentary material to relax but not suflicient to materially degrade said filamentary material a substantially vertically upward moving endless length of said filamentary material to turbulent flow of heated gas moving generally substantially vertically upward in a confined zone at a velocity sufficient to produce adequate turbulence for uniform and effective heat transfer but less than that at which said filamentary material is seriously disarranged or substantially elongated.

6. A method according to claim 5 in which said filamentary material is fed upwardly into the lower portion of the confined zone at a first substantially constant linear velocity and continuously removed from the upper portion of said confined zone at a second substantially constant linear velocity controlled at a value lower than said first linear velocity.

7. A method according to claim 6 wherein the gas velocity is such as to substantially eliminate tension on the filaments leaving the confined zone.

8. A method for continuously relaxing dry acrylic filamentary material comprising exposing for from 0.1 to 30 seconds a substantially vertically upward moving endless length of said filamentary material to turbulent flow of a gas heated to a temperature between 250 and 600 F. moving generally substantially vertically upward in a confined zone at a velocity sufficient to produce adequate turbulence for uniform and effective heat transfer but less than that at which said filamentary material is seriously disarranged or substantially elongated.

9. A method according to claim 8 wherein the heated gas is at a temperature between 400 and 500 F. and said filamentary material is exposed thereto for from 0.5 to 5.0 seconds.

References Cited UNITED STATES PATENTS 2,661,618 12/1953 Bessom 68-6 3,241,212 3/1966 Evans et al. 3,107,140 10/1963 Kurzke et al 264-342 3,156,752 11/1964 Cope 264-280 JULIUS FROME, Primary Examiner.

A. H. KOECKERT, Assistant Examiner.

US. Cl. X.R. 

